Concatenating tuples with a mix of runtime and comptime values fails

[alexnask]

const std = @import("std");
const assert = std.debug.assert;

fn consume_tuple(tuple: var) void {}

test "tuple concatenation" {
    const t1 = .{};

    var rt_var: u8 = 0;
    const t2 = .{rt_var}; // Same with var t2 = .{rt_var};

    // The following work.
    consume_tuple(t1 ++ t1);
    consume_tuple(.{} ++ .{});
    consume_tuple(.{0} ++ .{});
    consume_tuple(.{0} ++ .{1});
    consume_tuple(.{0, 1, 2} ++ .{u8, 1, noreturn});
    consume_tuple(t2 ++ t1);
    consume_tuple(t1 ++ t2);
    consume_tuple(t2 ++ t2);

    // The following error with message: "unable to evaluate constant expression"
    consume_tuple(.{rt_var} ++ t1);
    consume_tuple(.{} ++ .{rt_var});
    consume_tuple(.{u8} ++ .{rt_var});

    // The following error with message: "cannot assign to constant"
    consume_tuple(t2 ++ .{void});
    consume_tuple(t2 ++ .{0});
    consume_tuple(.{0} ++ t2);
    consume_tuple(.{void} ++ t2);
}

[mlarouche]

I have to do this workaround in a project to give a nice abstraction to call COM interface https://gist.github.com/mlarouche/c558881a9e51c45ef05577363de1602f#file-com_call-zig-L43

[alexnask]

Also relevant
Workaround in my std.interface PR:

zig/lib/std/interface.zig

Line 511 in 529d61f

// TODO: This errors with "cannot assign to constant"